Data rate control in soft handoff and during cell-switching

ABSTRACT

A method and apparatus for controlling a data rate of a transmission in a wireless communication system during handoff. Controlling the data rate includes receiving transmissions from a plurality of base stations, wherein at least one of the received transmissions includes an acknowledgement message. Then determining a rate control command included within transmissions of the base station that includes the acknowledgement message and using the command to control the data rate. Controlling the data rate also includes receiving transmissions from a plurality of base stations. Then determining a plurality of rate control commands included within the received transmissions from the plurality of base stations. The rate control commands are then combined and used to control the data rate.

CLAIM OF PRIORITY UNDER 35 U.S.C. §119

The present Application for Patent claims priority to ProvisionalApplication No. 60/511,254 entitled “DATA RATE CONTROL IN SHO AND DURINGCELL-SWITCHING” filed Oct. 14, 2003, and Provisional Application No.60/529,135, entitled “DATA RATE CONTROL IN SHO AND DURINGCELL-SWITCHING” filed Dec. 11, 2003 both of which are assigned to theassignee hereof and hereby expressly incorporated by reference herein.

BACKGROUND

1. Field

The invention relates generally to wireless communication, and morespecifically to data rate control in a wireless communication system.

2. Background

Wireless communication systems are used in many applications including,for example, paging, wireless local loops (WLL), Internet telephony,wireless telephone and satellite communication systems. An exemplaryapplication of a wireless telephone system is a cellular telephonesystem for remote subscribers which are often mobile. In a typicalcellular telephone system mobile subscribers, or mobile stations,transmit and receive signals from various base stations within awireless network infrastructure of the communication system as themobile station moves about.

Modern wireless communication systems, such as cellular telephonesystem, are typically designed to allow multiple users, or subscribers,to access a common communications medium. Various techniques have beendeveloped for these multiple access wireless communication systemsincluding code division multiple access (CDMA), time division multipleaccess (TDMA), and frequency division multiple access (FDMA). Thesemultiple access techniques encode, modulate, decode, and demodulatesignals transmitted and received between the multiple users and thewireless network infrastructure, thereby enabling simultaneouscommunication among multiple users and allowing for a relatively largecapacity for the communication systems.

In a wireless communication system based on CDMA, the available radiofrequency (RF) spectrum is shared efficiently among a number of users.Wireless communication systems typically transmit voice messages andmore recently, systems with enhanced capacity for data services are alsoavailable. An example of such a data-services communication system isthe high data rate (HDR) system that conforms to the TelecommunicationsIndustry Association/Electronic Industries Alliance (TIA/EIA) cdma2000High Data Rate Air Interface Specification IS-856, January 2002 (theIS-856 standard).

In a wireless communication system, such as one based on CDMA or one ofthe other multiple access techniques mentioned, users are often mobile.As a user moves about they may move out of the coverage area of a sectorof a base station or out of the coverage area of the base stationitself. As a user, also referred to as a mobile or a mobile station,moves in and out of different coverage areas such that the user leavesone coverage area and enters another, to maintain communications atechnique known as a “handoff” occurs. In a handoff the mobile stationbegins communicating with a sector of a base station, simply referred toas a base station, in the coverage area it is entering and terminatescommunication with the base station in the coverage area it is leaving.Using a technique referred to as “soft handoff” the mobile station willsimultaneously be in communication with the two base stations during thehandoff. In other words, the mobile will remain in communication withthe base station whose coverage area the mobile is leaving while alsoestablishing communication with the base station whose coverage area themobile is entering. In such a technique, both the base stations eitherjointly or independently decode the mobile stations transmission.Communicating with both base stations during the soft handoff reducesthe chance of a dropped call or other unintentional loss ofcommunication.

The data rate that can be supported by each of the two base stationsinvolved in a handoff may be different, for example, due to the level ofcongestion of the respective base station. The level of congestion in asystem may be determined by monitoring the data rates of users, and thereceived signal strength required to achieve a desired quality ofservice (QoS). The communication link from the mobile to the basestation is called the reverse link or uplink. In a wireless CDMA system,the reverse link capacity is interference-limited and one measure of thecell congestion is the total received power over the level of thethermal noise at a base station. The total received power over thethermal noise is commonly referred to as the “rise over thermal” (ROT)and corresponds to loading of the reverse link. Typically, it isdesirable to maintain the ROT near a predetermined value. If the ROT istoo high, the coverage of the cell, that is the distance over which thebase station of the cell can communicate, is reduced and the reverselink is less stable. A reduced cell coverage (such as from excessiveROT) can adversely affect the data rate that can be supported in thecell and the mobile stations at the edge of the cell may drop theircalls. The coverage of the cell reduces with high ROT due to an increasein the amount of transmit energy required at the mobile station toprovide a target energy level at the base station. Typically mobiles aresomewhat limited in the transmit power they have and thus a requirementto increase transmit power corresponds to a decreased range. A low ROTcan indicate that the reverse link is not heavily loaded, thusindicating that available data rate capacity is potentially beingwasted.

If a base station and a mobile involved in a handoff can supportdifferent data rates, then the data rate of the mobile station during ahandoff may not be optimal. For example, if the base station to whichthe mobile is handing off can support a higher data rate than is beingused by the mobile, then the mobile may be operating at a lower datarate than is possible, in which case there may be a waste of systemresources. If the base station to which the mobile is handing off cannotsupport a data rate as high as the mobile is operating with, then themobile can be causing increased interference with other users and couldbe degrading system performance. A form of rate management in asoft-handoff region can be achieved with co-ordination betweenbase-stations. However, the co-ordination between base-stations over theinfrastructure, or backhaul, may be slow or there may not be any supportto carry out the co-ordination between two base stations.

There is therefore a need in the art for improving distributed data ratecontrol during handoff in a wireless communication system.

SUMMARY

Embodiments disclosed herein address the above stated needs by providingmethods and apparatus for controlling a data rate of a transmission in awireless communication system during handoff. A mobile stationtransmission is received and decoded by multiple base stations in themobile station's handoff list. Any base station in the handoff list thatsuccessfully decodes a transmission sends an acknowledgement on thedownlink to the mobile station. The mobile station then determines arate control command based on transmissions from the base stations thatinclude an acknowledgement message. The mobile adjusts its data rate oftransmission in accordance with the rate control command.

In another aspect, a base station other than the base station that hassent the acknowledgement message may desire to communicate a desireddata rate command to the mobile station. The base station desiring tosend a rate command may be the primary base station that has the Qualityof Service (QoS) and other scheduling information, or the base stationmay be a non-primary base station that is heavily congested and maydesire to lower the rate of the transmission. The desired rate commandmay then be used by the mobile in determining the data rate oftransmission based on rate commands from the primary base station andthe non-primary base stations.

Controlling a data rate of transmission in a wireless communicationsystem during handoff can include receiving transmissions from aplurality of base stations, then determining a plurality of rate controlcommands from the respective received transmissions from the pluralityof base stations. The rate control commands may then be combined, andthe data rate of transmission adjusted in accordance with the combinedrate control commands. In the case of automatic repeat request (ARQ),non co-located base stations in handoff, may decode the transmissionsindependently and send acknowledgement (ACK) asynchronously. Theasynchronous ACKs leads to synchronization problems in transmitting arate control command. The base stations that do not ACK the transmissionmay not send a rate control command that may be interpreted as a HOLDstate of the rate control command. Aspects relating to this scenario aredescribed that provide effective ways of combining rate control commandsin handoff while being ACKed by non co-coordinating multiple basestations.

Combining the rate control commands can include applying weightingfactors to the received rate control commands. For example, the ratecontrol command of a primary base station can be assigned a largerweighting factor than commands from non-primary base stations. Combiningthe rate commands can also include establishing a rate control commandbased on a desired quality of service for the primary base station sothat the primary base station controls the data rate ramp-up andnon-primary base stations provide data rate control based on systemcongestion.

A further aspect of combining the rate control commands from multiplebase stations includes decreasing the data rate if at least one of thedata rate commands is for a decreased rate. Another aspect of combiningthe rate control commands includes maintaining the data rate if none ofthe data rate commands is for a decreased rate and at least one of thedata rate commands is a command to hold the data rate, for example ifthe data rate command is a null command. Yet another aspect of combiningthe rate control commands includes maintaining the data rate if none ofthe data rate commands is for a decreased rate, an increase rate or acommand to hold the data rate, but instead is a different command, suchas a null command. A further aspect of combining the rate controlcommands includes increasing the data rate if none of the data ratecommands is for a decreased rate or a command to hold the data rate andat least one data rate command is for an increased data rate.

Other features and advantages of the present invention should beapparent from the following description of exemplary embodiments, whichillustrate, by way of example, aspects of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows portions of a communication system 100 constructed inaccordance with the present invention.

FIG. 2 is a block diagram illustrating a wireless communication deviceduring a handoff between two base stations.

FIG. 3 is a flow chart illustrating a technique for combining ratecontrol indicators for common/group rate control.

FIG. 4 is a flow chart illustrating a technique for combining ratecontrol for a dedicated rate channel.

FIG. 5 is a block diagram of a wireless communication device constructedin accordance with an exemplary embodiment of the present invention.

DETAILED DESCRIPTION

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any embodiment described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments.

FIG. 1 shows portions of a communication system 100 constructed inaccordance with the present invention. The communication system 100includes infrastructure 101, multiple wireless communication devices(WCD) or mobile stations (MS) 104 and 105, and landline communicationdevices 122 and 124. In general, WCDs may be either mobile or fixed, and“WCD” will be used interchangeably with “MS” and “mobile.”

The infrastructure 101 includes components such as base stations 102,base station controllers 106, mobile switching centers 108, a switchingnetwork 120, and the like. In one embodiment, the base station 102 isintegrated with the base station controller 106, and in otherembodiments the base station 102 and the base station controller 106 areseparate components. Different types of switching networks 120 may beused to route signals in the communication system 100, for example, theswitching network 120 may be the public switched telephone network(PSTN).

The term “forward link” refers to the signal path from theinfrastructure 101 to a WCD 104, 105 and the term “reverse link” refersto the signal path from a WCD to the infrastructure. As shown in FIG. 1,WCDs 104 and 105 receive signals 132 and 136 on the forward link andtransmit signals 134 and 138 on the reverse link. In general, signalstransmitted from a WCD 104 and 105 are intended for reception at anothercommunication device, such as another remote unit, or at a landlinecommunication device 122 and 124, respectively, and are routed throughthe switching network 120. For example, if the signal 134 transmittedfrom an initiating WCD 104 is intended to be received by a destinationWCD 105, the signal is routed through the infrastructure and a signal136 is transmitted on the forward link to the destination WCD 105.Typically, a communication device, such as a WCD or a landlinecommunication device, may be both an initiator of and a destination forthe signals.

Examples of WCDs 104 include cellular telephones, wireless communicationenabled personal computers, and personal digital assistants (PDA), andother wireless devices. The communication system 100 may be designed tosupport one or more wireless standards. For example, the standards mayinclude standards referred to as TLA/EIA-95-B (IS-95), TIA/EIA-98-C(IS-98), cdma2000, Wideband CDMA (WCDMA), and others.

FIG. 2 is a block diagram illustrating a WCD 202 during a handoffbetween two base stations 204 and 206. As shown in FIG. 2, a WCD device202 is communicating with two base stations 204 and 206. In thisillustration, the primary base station 204 (BS1) is the base stationwhose coverage area the WCD 202 is currently in, and the non-primarybase station 206 (BS2) is the base station whose coverage area the WCD202 is entering.

The Third Generation Partnership Project 2 (3GPP2), a collaborativethird generation (3G) telecommunications specifications-setting projectcomprising North American and Asian interests for developing globalspecifications for ANSI/TIA/EIA-41 Cellular Radio telecommunicationIntersystem Operations network evolution of 3G, has received proposalsfor techniques for controlling data rate from one or many base stationsduring a hand off In accordance with these proposals, a base stationcontrolling the WCD sends a dedicated rate control command (a tri-statebit) which can either be UP, HOLD, or DOWN, signifying an increase, holdor decrease in rate or traffic-to-pilot ratio of the next transmission.If the WCD is in soft-handoff, the rate control commands can be receivedfrom different base stations. The rate control commands from differentbase stations can be combined to obtain an effective rate controlcommand. A drawback with this approach occurs when base station and WCDuses a technique referred to as hybrid automatic repeat request (HARQ)to improve the performance of the system. With HARQ enabled, a mobilestation sends same or different encoded copy of same packet till thebase station ACKs the transmission of the packet. A mobile stationtransmits a new packet at a new rate only when it has successfullytransmitted the previous packet or has transmitted the previous packetfor maximum number of times allowed. A mobile station has successfullytransmitted a packet if it receives acknowledgement (ACK) from at leasta single base station in its soft-handoff list. Due to this, a basestation in soft-handoff sends an UP or a DOWN rate control command onlywhen it has successfully decoded a packet and sends an ACK message onForward Acknowledgement Channel (F-ACKCH) of the base station. A HOLDcorresponds to no transmission on the rate control channel, and is powerefficient when the base station is not expecting a new transmission fromthe mobile station. Because the quality of transmissions received bydifferent base stations may be different, all base stations in a mobilestations soft-handoff list do not ACK the mobile at the same time. Thededicated rate control approach that works without HARQ may be redefinedin a system which uses both soft-handoff across different base stationsand HARQ for performance improvement. In an exemplary embodiment, a WCDmonitors the Forward Rate Control Channels (F-RCCH) of a base stationwhen it receives an acknowledgement message (ACK) on the ForwardAcknowledgement Channel (F-ACKCH) from the base station. A problem withthis approach can occur if the WCD 202 is in a soft handoff with theprimary base station 204 and the non-primary base station 206, and theWCD 202 receives an ACK only from the non-primary base station 206. Eventhough 204 is a primary base station and may be receiving moreinterference power from the WCD 202, the lightly loaded base station 206may decode the mobile station transmissions and send a rate controlcommand along with ACK requesting the WCD 202 to go UP in rate. If thisoccurs, the primary base station 204 may not able to control the rate ofthe WCD 202 via rate control commands.

An exception to this rule occurs after the last transmissioncorresponding to a data packet is sent, at which time the WCD monitorsall the F-RCCHs that are assigned to the WCD, regardless of whether ornot the WCD receives ACK from a BS. However, this scheme is verysensitive to control signaling errors, including reverse packet datacontrol channel (R-PDCCH) errors and forward-acknowledgement channel(F-ACKCH) errors. For example, R-PDCCH contains the control informationindicating the transmitted rate on the data/packet channel and thetransmission number (also called subpacket number) of the packet. TheSubpacket number indicates how many times the packet has beentransmitted and unsuccessful decoded at the base station. If thesubpacket number is equal to the maximum number of transmissionsallowed, then the current transmission on the packet channel is the lasttransmission to deliver the packet correctly to the BS. If a BS isunable to decode the R-PDCCH transmission from a WCD, the BS will beunaware that a subpacket is the last subpacket and that it should send arate control indicator to the MS. The MS would interpret the notransmission on F-RCCH to be a HOLD command. The HOLD command preventsthe WCD's rate from going up, even though the BS had no intention tosend a HOLD command and may be able to support higher date rate traffic.

In another embodiment, a mobile station monitors rate control commandonly from the primary base station. In this approach, non-primary basestations that may receive the interference from the mobile station arenot able to control the mobile station. Further, the mobile station ismoving, the mobile station may enter the service area of another basestation and may perform cell switching. During cell switching, the MScommunicates with the primary BS1 204 by sending a predetermined numberof switching frames indicating the non-primary BS2 206 will become theprimary base station. The switching between base stations is over whenthe MS receives a Switch End Indicator from the old primary BS1 204 orwhen a predetermined number of switching frames have been sent. The ratecontrol operation from the primary base station is not explicitlyspecified during the switching interval. Following is a description ofsome of the different techniques that can be used during soft handoffand cell switching where various problems are identified along with waysof addressing the problems.

Case 1

In this embodiment, an acknowledgement message (ACK) transmitted by abase station (BS) is received by the mobile station (MS) if the decodedtransmission corresponded to a packet that has not been sent the maximumnumber of times allowed. When the MS receives the ACK, it adjusts itsdata rate in accordance with the rate control bit(s) transmitted fromthe BS that ACK the transmission. The rate control bits received by themobile station from base stations that did not send the ACK are ignored.The mobile station monitors the rate control bit from all the basestations only when the previous transmission corresponded to a packetthat was transmitted a maximum number of times allowed.

There are several advantages to this approach. One is that if theprevious transmission is not the last transmission of a packet, the basestation can make a rate decision for the next transmission only if itACKs the previous transmission and expects new transmission. Also, whena base station doesn't ACK to the previous transmission from a mobilestation, it doesn't send anything on the rate control command, therebybeing power efficient while being sure that the rate control bit isignored and not interpreted as HOLD by the mobile station. Anotheradvantage is that this technique treats primary and non-primary basestations similarly. Therefore even when the primary base station changesduring cell switching, the rate control operation from the base stationsin soft-handoff is not influenced.

A problem with this technique can occur if there are load imbalancesbetween the base stations involved in the handoff. For example, aproblem can occur if the MS 202 is performing a soft handoff from aprimary BS 204 to a non primary BS 206 and the primary BS 204 is fullyloaded on the reverse link, say with a rise-over-thermal (ROT) of 7 dB,while the non-primary BS 206 has a relatively unloaded reverse-link, saywith an ROT of 2 dB. In this example of load imbalance, the MS 202 mayhave a better reverse-link with the non primary BS 204, since thetransmission from the MS 202 sees less interference. On the other hand,the reverse-link with the primary BS 204 may be weak, even though theprimary BS 204 may have a better forward-link to the MS 202. In thisscenario, the non-primary BS 206 can decode the MS 202 data packet andsend an ACK message to the MS 202. Since the non-primary BS 206 islightly loaded, it will send rate control bit(s) to increase the rate ofthe MS The primary BS 204, on the other hand, may be fully loaded, orcongested, and if it receives the MS 202 transmission at a lower SNR itmay not be able to decode the transmission and send an ACK. If theprimary BS 204 doesn't decode the transmission from MS 202, it doesn'tsend a rate control command to the MS 202, thereby losing control on theMS 202 transmission even though it receives more interference from theMS 202. If the MS 202 adjusts its data rate in accordance with the ratecontrol bit(s) sent by the lightly loaded BS 206 and increases its datarate, this can result in the congested primary BS 204 receiving more andmore interference from the MS 202, which it will be unable to adequatelycontrol. One solution to this problem is to have the primary BS 204decode the reverse packet data control channel (R-PDCCH) transmitted bythe MS 202 and check the data rate. If the MS 202 data rate is higherthan desired by the primary BS 204, the primary BS 204 can control theMS 202 transmission rate by requesting the non-primary BS 206 send RCbit(s) to the MS to decrease the MS data rate. The primary BS can sendthe request to the non primary BS directly, or through the communicationsystem infrastructure or backhaul, or in other ways appropriate to thesystem configuration.

Another problem with this technique (transmitting ACK from BS to MS) isthat both the primary BS 204 and the non-primary BS 206 should be awareof the QoS requirements of the mobile station. In most scenarios, anon-primary BS 206 that decodes the MS transmissions only rarely doesn'thave accurate QoS information and current requirements of the MS 202. Inthe absence of QoS requirements of the MS 202, the non-primary BS 206will not be able to send an appropriate rate control command to the MSunless the primary and non-primary BS co-ordinate via the backhaul toexchange this information.

Case II

In a second embodiment, the MS 202 adjusts its data rate in accordancewith RC bit(s) only from a primary BS 204. In other words, the MS 202adjusts its data rate in accordance with rate control bit(s) transmittedby the BS 204 currently designated as the primary BS even if an ACK isreceived from a non-primary BS 206. This technique has an advantage inthat if the primary BS does not want to change the data rate it will nottransmit a rate control bit(s), which is recognized as a HOLD command bythe MS and saves power on the BS forward link (FL). Thus, even if anon-primary BS 206 sends an ACK to the MS, the non-primary BS 206doesn't send rate control bit(s) to the MS. If the primary BS 204 iscongested, it can send DOWN rate control bit(s) and the MS will adjustits data rate accordingly even if a non-primary BS sends an ACK. Inaccordance with this embodiment, only a primary BS 204 needs to maintainthe QoS information and update the current requirements of the mobilestation.

A problem with this technique is that the non-primary BS 206 has nocontrol on the power it receives from the MS transmission that acts asinterference in reception of the other MS transmissions. In the case ofimbalance in propagation loss between forward link and reverse link, thenon-primary BS receives uncontrolled power from the MS. Under theembodiment, this problem can be addressed only when the non-primary BS206 requests the primary BS 204 to send a DOWN rate control command. Thenon-primary BS can send the request to the primary BS directly, orthrough the communication system infrastructure or backhaul, or in otherways appropriate to the system configuration.

In this rate control approach, the rate control algorithm is notcompletely defined in the mobile environment, when the MS 202 performscell switching. Before cell switching, the BS 204 is the primary BSwhile BS(s) 206 are the non-primary BS. Due to the mobile motion, thereceived signal from a non-primary BS 206 may become stronger than thesignal from the primary BS 204. Therefore, during cell switching, the MS202 transmits switching frames indicating 206 as its new primary BS.Before the switching frames are decoded by a base station, the BS 204regards itself as the primary BS for the MS 202. The problem occurs asthe MS 202 doesn't know when to regard BS 206 as its new primary BS andstart listening to the RC bit from the BS 206. This problem can beaddressed by having the MS 202 listen to rate control commands from boththe primary and non-primary BSs during cell switching and apply anOR-of-HOLD rule, where the MS will hold its data rate if either BS sendsa HOLD command, followed by applying the OR-of-DOWN rule, where the MSwill decrease its data rate if either BS commands a lower data rate.This approach gives the two BS more control over the MS 202transmission. In yet another embodiment that addresses this problem, theMS 202 listens to the rate control command only from the previousprimary BS 204 during the switching period. Only when last switchingindicator is sent or the MS 202 receives an acknowledgement of theswitch, it starts listening to the rate control command from the BS 206,the new primary BS. The BS 206 starts sending a rate control command assoon as it decodes the switching indicator. During the period, theswitch indicator is decoded by a BS to the time the MS receives anacknowledgement, the MS 202 listens to rate control bit(s) from the BS204 while the BS 206 sends the rate control bit(s). Because a lack oftransmission of rate control in the forward rate control channel(F-RCCH) from the BS 204 will be interpreted as HOLD by the MS 202,neither of the base stations will be able to change the rate of the MS202 during this interim period.

Case III

In this technique all cell sectors in the MS Active Set contribute tothe control of the MS data rate. This control is referred to as beingsymmetric, with the MS active Set members controlling the MS ramp-upwith an OR-of-DOWN rule followed by OR-of-HOLD rule. This technique hasan advantage that in all BSs communicating with the MS will contributeto the control the data rate of the MS transmission and so the ROT of abase station is less dramatically affected by any single MS and is morecontrolled. The technique operates similarly in both soft handoff andcell switching.

However, there are multiple problems with this technique, particularlyin scenarios where the multiple base stations in soft-handoff are notco-located and the decoding decisions of each are not known to otherbase stations by the time each BS makes its rate control decision. Forexample, in a system with hybrid automatic repeat request (HARQ), a newpacket is not transmitted by a MS until it receives ACK from one of thebase stations in soft-handoff or until the MS has transmitted a packetfor maximum allowed number of times. Therefore, when the previoustransmission is not the last transmission of a packet, the base stationdoesn't know whether it can schedule the MS for a new transmissionunless it decodes the previous transmission and ACKs the mobile station.In absence of this knowledge, the BS that doesn't ACK the mobilestations previous transmission may send a HOLD command to save power onthe forward link. However, by OR-of-HOLD rule, the MS will not be ableto increase its transmission rate unless all the base stations ACK themobile station at the same time. To circumvent this problem, the basestation that doesn't ACK the MS has to send an UP rate control commandall the time. This includes the times when MS is not transmittinganything on its reverse packet channel since the base station may not beable to distinguish no transmission from transmission not decoded. Thisis highly power inefficient, since each BS wastes the forward-link powerin sending an UP rate control command all those times, the base stationdoesn't send an ACK to the mobile station.

Case IV

In this embodiment, all cell sectors in the MS Active Set control the MSramp-up with an OR-of-DOWN rule followed by OR-of-HOLD rule, similar toCase III. However, unlike Case III, the control is asymmetric with theprimary BS providing the fundamental regulation of the MS data rateramp-up while the non-primary BSs provide congestion control. In otherwords, the primary sector sends a tri-state rate control (−1, 0, +1)command based on a desired QoS to the MS where no transmission (0) onrate control bit in rate control channel corresponds to the HOLD.Non-primary BSs sends an ON-OFF (−1, 0) rate control bit where notransmission (0) corresponds to UP or Don't Care while an ON statecorresponds to DOWN. The non-primary BS may send rate control commandbased on the congestion level of the respective non-primary BS. Thenon-primary BSs send an UP rate command to the MS if the non-primary BSis not congested and a DOWN rate command if the non-primary BS iscongested. For example, the non-primary BS may send an UP rate commandif its ROT indicates a low congestion level and a DOWN rate command ifits ROT indicates a high congestion level. In this embodiment, the ratecontrol bit from BS 206 may be common to all mobile stations 202 forwhich the BS 206 is non-primary.

Note that the above approach spends very little power on forward link ofnon-primary base stations since the UP command corresponds to notransmission on the rate control bit. A DOWN command from non-primary BSmay be send only if the system is severely congested, thereby providingsome control to the non-primary base stations, mentioned as a drawbackof the Case II. For example, if it is determined that the sector's ROTexceeds a predetermined value, such as 7 or 8 dB, then the non-primaryBS is considered to be congested and it sends a rate command of −1representing a DOWN rate command. Otherwise the non-primary BS isconsidered not congested and a rate command of 0 representing an UPcommand is sent. Because it is less likely for the system to beover-loaded for a long period of time, a DOWN command is send rarely.For most of the time, in this embodiment, a non-congested BS will send arate command of 0, which is the same as sending no command. Because thenon-congested BS sends no rate command, this technique therefore doesnot consume too much power from the non-primary sector.

Since this approach is asymmetric, the rate control in soft-handoffneeds to be specified as in case of cell-switching as in Case II. Duringcell switching a more conservative approach may be followed. In anembodiment, the MS decodes the rate control bit(s) from both the primaryBS 204 (the base station whose coverage area the MS is leaving) andnon-primary BS 206 (the base station whose coverage area the MS isentering) as a tri-state value of −1, 0, or 1 representing DOWN, HOLD,UP respectively. The cell switching operation begins when the MS sends aCELL_SWITCH_INDICATOR signal indicating BS 206 as its new primary BS.During the period from the beginning of the switching operation untilthe MS receives an END_SWITCH_INDICATOR (acknowledgement from the basestation indicating the switch operation is completed) orNUM_SOFT_SWITCHING_FRAMES indicators have been sent, the MS uses thesame logic to interpret rate control bit(s) from both the BS 204 and BS206. During this period, the MS applies OR-of-HOLD rule followed byOR-of-DOWN rule on the rate control commands from the BS 204 and BS 206.During the switching period, the MS 202 is not able to increase the rateeven if the new primary BS 206 sends an UP command due to OR-of-HOLDrule. Thus the approach is conservative during the switching period.

In yet another embodiment, during the switching period, the MS 202interprets the rate control command from BS 204 as a tri-state command(−1, 0, 1) while interpreting the rate control command from BS 206 as anON-OFF command (−1, 0). After the MS 202 receives an END_SWICH_INDICATORindicating BS 206 as its new primary BS or has sentNUM_SOFT_SWITCHING_FRAMES indicating the switch, the MS startsinterpreting rate control command from BS 204 as ON-OFF and rate controlcommand from BS 206 as a tri-state command. This approach is moreaggressive than the previously described techniques because it allowsthe BS 204 to increase the rate of the MS 202 before it decodes theCELL_SWITCH_INDICATOR. During the period, the CELL_SWITCH_INDICATOR isdecoded by a BS to the time the MS receives an END_SWICH_INDICATOR, theMS 202 is not able to increase the rate even if the new primary BS 206sends an UP command since the rate control command from the previousprimary BS 204 will be interpreted as HOLD by the MS.

Techniques of Combining Multiple Rate Control Indicators

A generalized technique for combining multiple rate control indicatorsincludes applying weighting factors to the different rate controlcommands received. For example, the primary base station may be assigneda larger weighting factor than non-primary base stations in a MS ActiveSet. The weighted rate command indicators can then be combined toproduce an aggregate rate command that is used to control the data rateof the MS. As discussed above, Case III corresponds to a case when equalweighting is applied to the rate control commands received from all thebase stations in mobile stations active set. Case IV is a special caseof weighting applied to the rate control commands where 0 weighting isapplied to the HOLD command from a non-primary BS. The different specialcases of the weighting technique for interpreting and combining the ratecontrol indicators the MS receives from its Active Set members aredescribed below.

Rate Control Combining Rules for Common/Group Rate Control

If a MS receives an ACK, or after its last subpacket, the MS decodesrate control, indicators from all the F-RCCHs that have been assigned tothe MS by members of the MS active set. Every rate control indicator hasthree states: DOWN, HOLD, and UP. The effect of a rate control commandis to change the authorized T/P by certain amount, where authorized T/Pis the maximum allowed “traffic to pilot” ratio that the mobile stationis allowed to transmit at and is used as an indication of the MS datarate that can be supported. In one embodiment, the MS combines all therate control indictors it receives based on the following OR-of-DOWNrules:

-   -   If any indicator is a DOWN, then the MS decreases its authorized        T/P by a predetermined amount from the current level.    -   If no indicator is a DOWN and at least one indictor is a HOLD,        then the MS maintains the current authorized T/P level.    -   Otherwise, all indicators are UP and the MS increases its        authorized T/P by a predetermined amount from the current level.

It is noted that the predetermined amounts that a MS increases ordecreases from its current authorized T/P may be the same, or they maybe different depending on the current authorized T/P of the MS.

Rate Control Combining Rules for Dedicated Rate Control

For dedicated rate control, if a MS receives an ACK on the F-ACKCH froma BS, it decodes all the F-RCCHs that are assigned to the MS, regardlessof whether or not the MS receives an ACK from a BS. The robustness of acommunication system that uses this reception procedure can be improvedusing the following weighting techniques.

-   -   The rate control indicator from the primary BS has three states:        RATE_DECREASE, RATE_HOLD, and RATE_INCREASE.    -   Rate control indicator from a non-primary BS has two states:        RATE_DECREASE and RATE_HOLD. This can be interpreted as a        weighting technique where the RATE_HOLD and RATE_INCREASE state        of rate control indicator from the non-primary BS is weighted by        a NULL factor.    -   MS combines desired rate control indictors based on the        following rules:        -   If any indicator is a RATE_DECREASE, then the MS decreases            its rate by a desired amount, for example by one.        -   If no indicator is a RATE_DECREASE and at least one indictor            is a RATE_HOLD, then the MS maintains the current rate.        -   If no indicator is a RATE_DECREASE or a RATE_HOLD, and at            least one indictor is a RATE_INCREASE, then the MS increases            its rate by a desired amount, for example by one.        -   Otherwise, all rate control indicators are RATE_HOLD and the            MS maintains the current rate.

It is noted that the MS combines desired rate control indicators whichcan include the rate control indicators of all of the MS active setmembers, or can include the rate control indicators of only some of theMS active set members.

Procedure During Cell Switching for Dedicated Rate Control:

After a MS initiates a cell switching operating by sending aCELL_SWITCH_INDICATOR, the MS assumes that the control rate indicatorsfrom both the old primary BS and the new primary BS each have threestates: RATE_DECREASE, RATE_HOLD, and RATE_INCREASE. The rate controlindicators from all other non-primary BS remains unchanged, and have twostates: RATE_DECREASE and NULL_INDICATION. The rate control indicatorsare combined using the same combining rules described immediately above.

Upon receiving an END_SWITCH_INDICATOR, or after sendingNUM_SOFT_SWITCHING_FRAMES, the MS assumes that the rate controlindicator from the new primary BS has three states: RATE_DECREASE,RATE_HOLD, and RATE_INCREASE. The rate control indicators from all othernon-primary BSs, including the old primary BS, have two states:RATE_DECREASE and NULL_INDICATION. The rate control indicators arecombined based on the same combining rules described immediately above.

An alternative approach is to define the states of the F-RCCH from anon-primary BS “on the fly” based on what is received on thecorresponding F-ACKCH from the associated BS. For this approach thefollowing procedure is used:

-   -   If an ACK is received from an F-ACKCH, then the MS interprets        that the corresponding F-RCCH from the same non-primary BS has        three states: RATE_DECREASE, RATE_HOLD, and RATE_INCREASE.    -   If no ACK is received from an F-ACKCH (after last subpacket),        then the MS interprets that the corresponding F-RCCH from the        same non-primary BS has two states: RATE_DECREASE and        NULL_INDICATION.

All other rules for combining remain the same as described immediatelyabove.

FIG. 3 is a flow chart illustrating a technique for combining ratecontrol indicators for common/group rate control. In a common/group ratecontrol scheme, one rate control command is sent that is monitored byall the mobile stations or a group of mobile stations in the coveragearea of the base station. Flow begins in block 302. In block 304 a MSdecodes rate control indicators received from members of the MS activeset of a BS. In block 306 the MS determines if any of the rate controlindicators is an AUTHORIZED_T2P_DECREASE (DOWN rate control command). Ifat least one of the indicators is an AUTHORIZED_T2P_DECREASE, a “YES”outcome, then flow continues to block 308. In block 308 the MS decreasesits authorized T/P (Traffic to Pilot) level by a predetermined amount.Flow then continues to block 310 where the combining process ends.

Returning to block 306, if none of the indicators is anAUTHORIZED_T2P_DECREASE, a “NO” outcome, then flow continues to block312. In block 312, the MS determines if any of the rate controlindicators is an AUTHORIZED_T2P_HOLD (HOLD rate control command). If atleast one of the indicators is an AUTHORIZED_T2P_HOLD, a “YES” outcome,then flow continues to block 314. In block 314 the MS maintains itscurrent authorized T/P level. Flow then continues to block 310 where theprocess ends.

Returning to block 312, if none of the indicators is anAUTHORIZED_T2P_HOLD, a “NO” outcome, then all of the indicators must beAUTHORIZED_T2P_INCREASE (UP rate control command) because the indicatorscan only be one of three values, either AUTHORIZED_T2P_DECREASE,AUTHORIZED_T2P_HOLD, or AUTHORIZED_T2P_INCREASE. Therefore, in block312, if none of the indicators is an AUTHORIZED_T2P_HOLD, flow continuesto block 316. In block 316 the MS increases its authorized T/P by apredetermined amount. Flow then continues to block 310 where the processends.

FIG. 4 is a flow chart illustrating a technique for combining ratecontrol for a dedicated rate control approach. In the dedicated ratecontrol approach, a separate rate control command specific to eachmobile station is sent for all MS. Flow begins in block 402. In block404 a MS decodes rate control indicators received from primary andnon-primary BS. A rate control indicator from a primary BS can either bea RATE_DECREASE, RATE_HOLD, or RATE_INCREASE. A rate control indicatorfrom a non-primary BS can be either RATE_DECREASE or NULL_INDICATION.Flow continues to block 406. In block 406 the MS determines if any ofthe rate control indicators is a RATE_DECREASE. If at least one of theindicators is an RATE_DECREASE, a “YES” outcome at block 406, then flowcontinues to block 408. In block 408 the MS decreases its data rate. Forexample, the MS may decrease its data rate by a value of one. Flow thencontinues to block 410 where the combining process ends.

Returning to block 406, if none of the indicators is an RATE_DECREASE, a“NO” outcome at block 406, then flow continues to block 412. In block412, the MS determines if the rate control indicator from the primary BSis a RATE_HOLD. If at least one of the indicators is an RATE_HOLD, thenflow continues to block 414. In block 414 the MS maintains its currentdata rate. Flow then continues to block 410 where the process ends.

Returning to block 412, if none of the indicators is a RATE_HOLD, a “NO”outcome, then flow continues to block 416. In block 416, since none ofthe indicators is RATE_DECREASE and the indicator from primary BS is nota RATE_HOLD, the MS increases its data rate. Flow then continues toblock 410 where the process ends.

FIG. 5 is a block diagram of a wireless communication device constructedin accordance with an exemplary embodiment of the present invention. Thecommunication device 502 includes a network interface 506, digitalsignal processor (DSP) 508, a host processor 510, a memory device 512, aprogram product 514, and a user interface 516.

Signals from the infrastructure are received by the network interface506 and sent to the host processor 510. The host processor 510 receivesthe signals and, depending on the content of the signal, responds withappropriate actions. For example, the host processor 510 may determine adata rate in accordance with the received signals itself, or it mayroute the received signals to the DSP 508 for determining a data rate.

In one embodiment, the network interface 506 may be a transceiver and anantenna to interface to the infrastructure over a wireless channel. Inanother embodiment, the network interface 506 may be a network interfacecard used to interface to the infrastructure over landlines.

Both the host processor 510 and the DSP 508 are connected to a memorydevice 512. The memory device 512 may be used to store data duringoperation of the WCD, as well as store program code that will beexecuted by the host processor 510 or the DSP 508. For example, the hostprocessor, DSP, or both, may operate under the control of programminginstructions that are temporarily stored in the memory device 512. Thehost processor and DSP also can include program storage memory of theirown. When the programming instructions are executed, the host processor510 or DSP 508, or both, perform their functions, for examplecompression or decompression of data packets. Thus, the programmingsteps implement the functionality of the respective host processor orCPU, and DSP, so that the host processor and DSP can each be made toperform the functions of determining a data rate as desired. Theprogramming steps may be received from a program product 514. Theprogram product 514 may store, and transfer the programming steps intothe memory 512 for execution by the host processor, CPU, or both.

The program product 514 may be semiconductor memory chips, such as RAMmemory, flash memory, ROM memory, EPROM memory, EEPROM memory,registers, as well as other storage devices such as a hard disk, aremovable disk, a CD-ROM, DVD storage, or any other form of storagemedium known in the art that may store computer readable instructions.Additionally, the program product 514 may be the source file includingthe program steps that is received from the network and stored intomemory and is then executed. In this way, the processing steps necessaryfor operation in accordance with the invention may be embodied on theprogram product 514. In FIG. 5, the exemplary storage medium is showncoupled to the host processor such that the host processor may readinformation from, and write information to, the storage medium.Alternatively, the storage medium may be integral to the host processor.

The user interface 516 is connected to both the host processor 510 andthe DSP 508. For example, the user interface may include a keypad, orspecial function keys or buttons, that are routed to the host processor510 and may be used by a user to request specific operation by theinitiating device. The user interface 516 may also include a speakerthat is connected to the DSP 510 and used to output audio data to theuser.

Those of skill in the art will understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill in the art will further appreciate that the variousillustrative logical blocks, modules, circuits, and algorithm stepsdescribed in connection with the embodiments disclosed herein may beimplemented as electronic hardware, computer software, or combinationsof both. To clearly illustrate this interchangeability of hardware andsoftware, various illustrative components, blocks, modules, circuits,and steps have been described above generally in terms of theirfunctionality. Whether such functionality is implemented as hardware orsoftware depends upon the particular application and design constraintsimposed on the overall system. Skilled artisans may implement thedescribed functionality in varying ways for each particular application,but such implementation decisions should not be interpreted as causing adeparture from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The method or technique described in connection with the embodimentsdisclosed herein may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such that theprocessor may read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. The processor and the storage medium may reside in anASIC. The ASIC may reside in a user terminal. In the alternative, theprocessor and the storage medium may reside as discrete components in auser terminal.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

1. A method of controlling a data rate of a transmission in a wirelesscommunication system during handoff, the method comprising: receivingtransmissions from a plurality of base stations, wherein at least one ofthe received transmissions includes an acknowledgement message;determining a rate control command in accordance with the receivedtransmissions that includes the acknowledgement message; and adjustingthe data rate of the transmission during handoff in accordance with therate control command.
 2. A method as defined in claim 1, wherein thereceiving, determining and adjusting are performed in a mobile station.3. A method as defined in claim 1, wherein the receiving, determiningand adjusting are performed in a base station.
 4. A method as defined inclaim 1, wherein the acknowledgement message is received from only oneof the plurality of base stations.
 5. A method as defined in claim 1,wherein more than one of the plurality of base stations transmit areceived acknowledgement message and the data rate during handoff isadjusted in accordance with the rate control associated with the lastreceived transmission that included the acknowledgement message.
 6. Amethod as defined in claim 1, wherein one of the plurality of basestations other than the base station from which the acknowledgementmessage was received communicates a desired data rate command to thebase station from which the acknowledgement message was received.
 7. Amethod as defined in claim 6, wherein the base station from which theacknowledgement message was received uses the desired data rate commandin determining the rate control command.
 8. A method of controlling adata rate of a transmission in a wireless communication system duringhandoff, the method comprising receiving transmissions from a pluralityof base stations; determining a rate control command in accordance withthe received transmissions from the plurality of base stations; andadjusting the data rate of a transmission in accordance with thedetermined rate control command.
 9. A method as defined in claim 8,wherein determining the rate control command includes applying weightingfactors to rate control commands derived from the receivedtransmissions.
 10. A method as defined in claim 9, wherein one of theplurality of base stations is designated as a primary base station. 11.A method as defined in claim 10, wherein the rate control commandderived from the primary base station is assigned a larger weightingfactor than the rate control command derived from non-primary basestations.
 12. A method as defined in claim 8, wherein a primary basestation sends a transmission specifying a rate control command based ona desired quality of service.
 13. A method as defined in claim 8,wherein determining the rate control command further comprises combininga plurality of rate commands.
 14. A method as defined in claim 13,wherein combining the plurality of rate commands transmission is in anasymmetric operation.
 15. A method as defined in claim 14, wherein aprimary base station controls data rate ramp-up.
 16. A method as definedin claim 14, wherein non-primary base stations provide data rate controlof system congestion.
 17. A method as defined in claim 13, whereincombining the plurality of rate commands further comprises decreasingthe data rate if at least one data rate command is for a decreased rate.18. A method as defined in claim 13, wherein combining the plurality ofrate commands further comprises maintaining the data rate if none of thedata rate commands is for a decreased rate and at least one data ratecommand is a command to hold the data rate.
 19. A method as defined inclaim 13, wherein combining the plurality of rate commands furthercomprises maintaining the data rate if none of the data rate commands isfor a decreased rate, an increase rate or a command to hold the datarate.
 20. A method as defined in claim 13, wherein combining theplurality of rate commands further comprises increasing the data rate ifnone of the data rate commands is for a decreased rate or a command tohold the data rate and at least one data rate command is for anincreased data rate.
 21. An apparatus for controlling a data rate of atransmission in a wireless communication system during handoff, theapparatus comprising: a receiver configured to receive transmissionsfrom a plurality of base stations, wherein at least one of the receivedtransmissions includes an acknowledgement message; and a processorconfigured to determine a rate control command in accordance with thereceived transmissions that includes the acknowledgement message, and toadjust the data rate of the transmission during handoff in accordancewith the rate control command.
 22. An apparatus as defined in claim 21,wherein the receiver and processor are included in a mobile station. 23.An apparatus for controlling a data rate of a transmission in a wirelesscommunication system during handoff, the apparatus comprising a receiverconfigured to receive transmissions from a plurality of base stations; aprocessor configured to determine a rate control command in accordancewith the received transmissions from the plurality of base stations andto adjust the data rate of a transmission in accordance with thedetermined rate control commands.
 24. An apparatus as defined in claim23, wherein determining the rate control commands further comprisescombining rate control commands derived from the transmissions receivedfrom the plurality of base stations.
 25. An apparatus as defined inclaim 24, wherein combining the rate control commands includes applyingweighting factors to rate control commands.
 26. An apparatus as definedin claim 24, wherein combining the rate control commands is in anasymmetric operation.
 27. An apparatus as defined in claim 26, wherein aprimary base station controls the data rate ramp-up.
 28. An apparatus asdefined in claim 26, wherein non-primary base stations provide data ratecontrol of system congestion.
 29. An apparatus as defined in claim 24,wherein combining the rate control commands further comprises decreasingthe data rate if at least one data rate command is for a decreased rate.30. An apparatus as defined in claim 24, wherein combining the ratecontrol commands further comprises maintaining the data rate if none ofthe data rate commands is for a decreased rate and at least one datarate command is a command to hold the data rate.
 31. An apparatus asdefined in claim 24, wherein combining the rate control commands furthercomprises maintaining the data rate if none of the data rate commands isfor a decreased rate, an increase rate or a command to hold the datarate.
 32. An apparatus as defined in claim 24, wherein combining therate control commands further comprises increasing the data rate if noneof the data rate commands is for a decreased rate or a command to holdthe data rate and at least one data rate command is for an increaseddata rate.
 33. A computer readable media embodying a method ofcontrolling a data rate of a transmission in a wireless communicationsystem during handoff, the method comprising: receiving transmissionsfrom a plurality of base stations, wherein at least one of the receivedtransmissions includes an acknowledgement message; determining a ratecontrol command in accordance with the received transmissions thatincludes the acknowledgement message; and adjusting the data rate of thetransmission during handoff in accordance with the rate control command.34. A computer readable media embodying a method of controlling a datarate of a transmission in a wireless communication system duringhandoff, the method comprising receiving transmissions from a pluralityof base stations; determining a rate control command in accordance withthe received transmissions from the plurality of base stations; andadjusting the data rate of a transmission in accordance with thedetermined rate control commands.
 35. A method of controlling a datarate of a transmission in a wireless communication system duringhandoff, the method comprising: means for receiving transmissions from aplurality of base stations, wherein at least one of the receivedtransmissions includes an acknowledgement message; means for determininga rate control command in accordance with the received transmissionsthat includes the acknowledgement message; and means for adjusting thedata rate of the transmission during handoff in accordance with the ratecontrol command.